title: Refined crystal structure of beta-lactamase from Citrobacter freundii indicates a mechanism for beta-lactam hydrolysis.
abstract: Beta-Lactamases (EC 3.5.2.6, 'penicillinases') are a family of enzymes that protect bacteria against the lethal effects of cell-wall synthesis of penicillins, cephalosporins and related antibiotic agents, by hydrolysing the beta-lactam antibiotics to biologically inactive compounds. Their production can, therefore, greatly contribute to the clinical problem of antibiotic resistance. Three classes of beta-lactamases--A, B and C--have been identified on the basis of their amino-acid sequence; class B beta-lactamases are metalloenzymes, and are clearly distinct from members of class A and C beta-lactamases, which both contain an active-site serine residue involved in the formation of an acyl enzyme with beta-lactam substrates during catalysis. It has been predicted that class C beta-lactamases share common structural features with D,D-carboxypeptidases and class A beta-lactamases, and further, suggested that class A and class C beta-lactamases have the same evolutionary origin as other beta-lactam target enzymes. We report here the refined three-dimensional structure of the class C beta-lactamase from Citrobacter freundii at 2.0-A resolution and confirm the predicted structural similarity. The refined structure of the acyl-enzyme formed with the monobactam inhibitor aztreonam at 2.5-A resolution defines the enzyme's active site and, along with molecular modelling, indicates a mechanism for beta-lactam hydrolysis. This leads to the hypothesis that Tyr 150 functions as a general base during catalysis.
authors.affiliation: Central Research Unit, F. Hoffmann-La Roche Co. Ltd, Basel, Switzerland.
authors.forename: C
authors.initials: C
authors.lastname: Oefner
authors.forename: A
authors.initials: A
authors.lastname: D'Arcy
authors.forename: J J
authors.initials: JJ
authors.lastname: Daly
authors.forename: K
authors.initials: K
authors.lastname: Gubernator
authors.forename: R L
authors.initials: RL
authors.lastname: Charnas
authors.forename: I
authors.initials: I
authors.lastname: Heinze
authors.forename: C
authors.initials: C
authors.lastname: Hubschwerlen
authors.forename: F K
authors.initials: FK
authors.lastname: Winkler
mesh_terms: D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000096:biosynthesis; D001665:Binding Sites; D002954:Citrobacter / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D001618:beta-Lactamases / Q000378:metabolism*; D047090:beta-Lactams
chemical_list: D000900:Anti-Bacterial Agents; D047090:beta-Lactams; D001618:beta-Lactamases